Anisotropic iron nitride permanent magnets

ABSTRACT

Disclosed herein is a permanent magnet comprising: a plurality of aligned iron nitride nanoparticles wherein the iron nitride nanoparticles include α″-Fe 16 N 2  phase domains; wherein a ratio of integrated intensities of an α″-Fe 16 N 2  (004) x-ray diffraction peak to an α″-α″-Fe 16 N 2  (202) x-ray diffraction peak for the aligned iron nitride nanoparticles is greater than at least 7%, wherein the diffraction vector is parallel to alignment direction, and wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction that is greater than a squareness measured perpendicular to the alignment direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 17/182,066; filed Feb. 22, 2021, which claims priority to U.S.Provisional Application No. 62/979,668, filed Feb. 21, 2020, and U.S.Provisional Application No. 63/080,144, filed Sep. 18, 2020. The entiredisclosure of each application is incorporated by reference herein forall purposes.

FIELD OF THE INVENTION

The disclosed inventions are in the field of iron nitride magneticmaterials.

BACKGROUND OF THE INVENTION

Permanent magnets can provide high efficiency and reliability forrenewable energy technologies. Rare earth permanent magnets aregenerally encumbered by supply constraints and high prices. Novelmagnets formed from more abundant and less strategically importantelements are desired to replace rare earth magnets; materials includingα″-Fe₁₆N₂ are desirable candidates for such “rare-earth-free” magnets.

Permanent nanocomposite magnets may be produced from individualnanoparticles by consolidation. A binder may be used that fixes thenanoparticles in a matrix. If the nanoparticles have sufficiently largemagnetic anisotropy, an external force may be used to align thenanoparticles prior to and/or during consolidation. However,electrostatic and electromagnetic forces generally combine to causenanoparticles to form agglomerates that are typically porous, relativelylarge clusters of nanoparticles. These agglomerates may hinder theability of individual nanoparticles to rotate in response to an externalalignment force.

Thus, there remains a need for rare-earth-free permanent anisotropicmagnetic materials that overcome the tendency of nanoparticles toagglomerate during processing for making rare-earth free magnets. Thedisclosed inventions are directed to these and other important needs.

SUMMARY

In various examples, the disclosure describes permanent magnetscomprising a plurality of aligned iron nitride nanoparticles. Thealigned iron nitride nanoparticles may include α″-Fe₁₆N₂ phase domains.The iron nitride nanoparticles may exhibit a ratio of integratedintensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂(202) x-ray diffraction peak for the aligned iron nitride nanoparticlesis greater than at least 7%, where the diffraction vector is parallel toalignment direction. Furthermore, the iron nitride nanoparticles mayexhibit a squareness measured parallel to the alignment direction thatis greater than a squareness measured perpendicular to the alignmentdirection.

This disclosure also describes dispersions comprising the disclosed ironnitride nanoparticles and a suitable solvent.

Moreover, the present disclosure describes nanocomposites comprising thedisclosed iron nitride nanoparticles and a suitable binder.

In addition, the disclosure describes workpieces including theanisotropic iron nitride nanoparticles made by any of the techniquesdescribed herein. Workpieces may take a number of forms, such as a wire,rod, tape, bar, conduit, hollow conduit, film, sheet, or fiber, each ofwhich may have a wide variety of cross-sectional shapes and sizes, aswell as any combinations thereof.

Methods of forming the disclosed iron nitride nanoparticles and articlescomprised thereof are further described herein.

The general description and the following detailed description areexemplary and explanatory only and are not restrictive of the invention,as defined in the appended claims. Other aspects of the presentinvention will be apparent to those skilled in the art in view of thedetailed description of the invention as provided herein. The details ofone or more examples are set forth in the accompanying drawings and thedescription below. Other features, objects, and advantages will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

The summary, as well as the following detailed description, is furtherunderstood when read in conjunction with the appended drawings. For thepurpose of illustrating the invention, there are shown in the drawingsexemplary embodiments of the invention; however, the disclosure is notlimited to the specific methods, compositions, and devices disclosed. Inaddition, the drawings are not necessarily drawn to scale. In thedrawings:

FIG. 1 presents the hysteresis loops measured on sample S5. Themeasurements were made in directions both parallel to (solid line) andperpendicular to (dashed line) the alignment field direction. FIG. 1Ashows the region of the hysteresis loops centered where the descendingcurves intersect the vertical axis.

FIG. 2 presents X-Ray diffraction pattern measured on sample S5. Theorientation of the diffraction vector is parallel to the alignmentdirection.

FIG. 3 presents the hysteresis loops measured on a comparative sampleCS6. The measurements were made in directions both parallel to (solidline) and perpendicular to (dashed line) the alignment field direction.FIG. 3A shows the region of the hysteresis loops centered where thedescending curves intersect the vertical axis.

FIG. 4 presents the X-Ray diffraction pattern measured on a comparativesample CS6. The orientation of the diffraction vector is parallel to thealignment direction.

FIG. 5 presents the hysteresis loops measured on sample S8. Themeasurements were made in directions both parallel to (solid line) andperpendicular to (dashed line) the alignment field direction. FIG. 5Ashows the region of the hysteresis loops centered where the descendingcurves intersect the vertical axis.

FIG. 6 presents the X-Ray diffraction pattern measured on sample S8. Theorientation of the diffraction vector is parallel to the alignmentdirection.

FIG. 7 presents hysteresis loops measured on sample S16. Themeasurements were made in directions both parallel to (solid line) andperpendicular to (dashed line) the alignment field direction. Thediamagnetic contribution from the sample holder was subtracted from thehysteresis loops. FIG. 7A shows the region of the hysteresis loopscentered where the descending curves intersect the vertical axis.

FIG. 8 presents the X-Ray diffraction pattern measured on sample S16.The orientation of the diffraction vector is parallel to the alignmentdirection.

FIG. 9 shows exemplary embodiments in accordance to the presentinvention.

FIG. 10 shows deagglomeration of nanoparticles in accordance toexemplary embodiments.

FIG. 11 presents a description of agglomerated nanoparticles.

FIG. 12 presents a description of agglomerated nanoparticles.

FIG. 13 shows the effects of milling on magnetic properties.

FIG. 14 shows the effect of milling phase distribution.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure may be understood more readily by reference tothe following detailed description taken in connection with theaccompanying figures and examples, which form a part of this disclosure.It is to be understood that this disclosure is not limited to thespecific devices, methods, applications, conditions or parametersdescribed and/or shown herein, and that the terminology used herein isfor the purpose of describing particular examples and is not intended tobe limiting of the claims. When a range of values is expressed, anotherexample includes from the one particular value and/or to the otherparticular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another example. All ranges areinclusive and combinable. Further, a reference to values stated in arange includes each and every value within that range.

It is to be appreciated that certain features of the disclosure whichare, for clarity, described herein in the context of separate examples,may also be provided in combination in a single example. Conversely,various features of the disclosure that are, for brevity, described inthe context of a single example, may also be provided separately or inany sub-combination.

It is also to be understood that the terminology used herein is for thepurpose of describing particular aspects only and is not intended to belimiting. As used in the specification and in the claims, the term“comprising” can include the embodiments “consisting of” and “consistingessentially of” Unless defined otherwise, all technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this disclosure belongs. In thisspecification and in the claims which follow, reference will be made toa number of terms which shall be defined herein.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a thermoplasticpolymer component” includes mixtures of two or more thermoplasticpolymer components. As used herein, the term “combination” is inclusiveof blends, mixtures, alloys, reaction products, and the like.

Ranges can be expressed herein as from one value (first value) toanother value (second value). When such a range is expressed, the rangeincludes in some aspects one or both of the first value and the secondvalue. Similarly, when values are expressed as approximations, by use ofthe antecedent ‘about,’ it will be understood that the particular valueforms another aspect. It will be further understood that the endpointsof each of the ranges are significant both in relation to the otherendpoint, and independently of the other endpoint. It is also understoodthat there are a number of values disclosed herein, and that each valueis also herein disclosed as “about” that particular value in addition tothe value itself. For example, if the value “10” is disclosed, then“about 10” is also disclosed. It is also understood that each unitbetween two particular units are also disclosed. For example, if 10 and15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

As used herein, the terms “about” and “at or about” mean that the amountor value in question can be the designated value, approximately thedesignated value, or about the same as the designated value. It isgenerally understood, as used herein, that it is the nominal valueindicated ±10% variation unless otherwise indicated or inferred. Theterm is intended to convey that similar values promote equivalentresults or effects recited in the claims. That is, it is understood thatamounts, sizes, formulations, parameters, and other quantities andcharacteristics are not and need not be exact, but can be approximateand/or larger or smaller, as desired, reflecting tolerances, conversionfactors, rounding off, measurement error and the like, and other factorsknown to those of skill in the art. In general, an amount, size,formulation, parameter or other quantity or characteristic is “about” or“approximate” whether or not expressly stated to be such. It isunderstood that where “about” is used before a quantitative value, theparameter also includes the specific quantitative value itself, unlessspecifically stated otherwise.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event or circumstance can or cannot occur, andthat the description includes instances where said event or circumstanceoccurs and instances where it does not. For example, the phrase“optional additional processes” means that the additional processes canor cannot be included and that the description includes methods thatboth include and that do not include the additional processes.

Iron nitride nanoparticles can be conveniently produced by controlledreduction and nitriding of iron oxide nanoparticle precursors. Ironoxide nanoparticle precursors can be produced by a variety of means andare typically supplied as dried powders comprised of clumps ofagglomerated nanoparticles. In a low temperature processing route, ironoxide nanoparticle agglomerates can be first reduced to elemental ironby annealing in a hydrogen containing atmosphere to produce ironnanoparticles. The iron nanoparticles can then transformed to ironnitride by annealing in an ammonia atmosphere. Optionally, a passivationtreatment can be provided in which the iron nitride nanoparticles arecoated with a thin layer of a stable metal oxide. These process stepsproduce isotropic agglomerates of iron nitride nanoparticles that arecharacterized by high saturation magnetization and moderate coercivity.This combination of magnetic properties makes iron nitride nanoparticlesuseful as a component of a permanent magnet.

Aligned Nanoparticles and Permanent Magnets Formed Therefrom

Permanent nanocomposite magnets may be produced from individualnanoparticles via a suitable consolidation process. Where thenanoparticles have a sufficiently large magnetic anisotropy, an externalforce may be used to align the nanoparticles prior to and/or duringconsolidation. However, electrostatic and electromagnetic forcesgenerally combine to cause nanoparticles to form agglomerates that aretypically porous clusters of nanoparticles that can be hundreds ofmicrons in diameter. It is thus difficult to deagglomerate thenanoparticles to the extent needed to provide the individualnanoparticles the ability to rotate in response to an externally appliedalignment force. Furthermore, the deagglomeration process raises thespecific surface area of the assembly of nanoparticles. This increase insurface area may result in more reactive nanoparticles, which are, inturn, more susceptible to oxidation, decomposition, and re-sinteringprior to alignment. Accordingly, these nanoparticles are not aligned,and when consolidated may form an isotropic nanocomposite permanentmagnet.

Isotropic nanocomposite permanent magnets have low energy product andremnant magnetization, which is attributed to a low squareness. As theseconventional nanoparticle agglomerates are isotropic, they are unable tobe aligned with an external force resulting in the described low remnantmagnetization and low squareness. The aligned nanocomposite permanentmagnet of the present disclosure may overcome the tendency ofnanoparticles to form randomly oriented agglomerates. As such, thepresent disclosure provides anisotropic nanocomposite permanent magnetsthat exhibit enhanced squareness.

According to various aspects, anisotropic nanocomposite permanentmagnets may be formed by aligning the nanoparticles that comprise thenanocomposite. The anisotropy of the resulting nanocomposite is thus thevolume weighted average of the anisotropy of each constituentnanoparticle and the nanocomposite will have a preferred orientation ofits magnetization vector. The nanocomposite's remnant magnetization isthe sum of the projections of each nanoparticle's magnetization vectoronto the preferred orientation vector. As such, the disclosednanocomposite may overcome the inherent tendency of magneticnanoparticles to form agglomerates of multiple, randomly orientednanoparticles.

In various aspects, the present disclosure provides a permanent magnetcomprising a plurality of aligned iron nitride nanoparticles. Suchpermanent magnets provide a high energy product and feature preferredmagnetization directions of each individual nanoparticle or grain thatcomprises the magnet's microstructure. This results in the remnantmagnetization (Mr) of the magnet being a large fraction of the magnet'ssaturation magnetization (MSat). The ratio of the remnant magnetizationto the saturation magnetization (Mr/MSat) is defined as the squareness(S). A permanent magnet may be considered anisotropic if the value ofthe squareness measured parallel to the alignment direction is greaterthan the squareness measured perpendicular to the alignment direction.Squareness is thus enhanced by the formation of a nanocompositepermanent magnet comprised of aligned, anisotropic nanoparticles. Thisalignment results in the nanocomposite having a preferred magnetizationdirection. The remnant magnetization and energy product of thenanocomposite is thereby enhanced because of the alignment of themagnetic nanoparticles arranged within the composite.

As provided herein, the disclosed aligned nanoparticles may compriseα″-Fe₁₆N₂ phase domains. Throughout this disclosure, the terms Fe₁₆N₂,α″-Fe₁₆N₂, α″-Fe₁₆N₂ phase, and α″-Fe₁₆N₂ phase domain, for example, maybe used interchangeably to refer to a α″-Fe₁₆N₂ phase domain within amaterial. In some examples, an anisotropic nanoparticle formed accordingto techniques disclosed herein may include at least one Fe₁₆N₂ ironnitride crystal. In further examples, such an anisotropic particle mayinclude a plurality of iron nitride crystals, at least some (or all) ofwhich are Fe₁₆N₂ crystals. The disclosed anisotropic iron nitridenanoparticles including Fe₁₆N₂ may have enhanced magnetic properties,including, for example, at least one of enhanced squareness, magneticorientation, or energy product, as compared to conventional isotropicparticles including Fe₁₆N₂. Thus, for example, the disclosed alignedanisotropic particles including Fe₁₆N₂ may be desirable for permanentmagnet applications.

Alignment of the disclosed nanoparticles may be detected by observing alarger squareness in hysteresis loops measured in a direction parallelto the alignment field than in a loop measured perpendicular to thealignment field. As such, nanoparticles of the present disclosure mayexhibit a preferred alignment where squareness in hysteresis loopsmeasured in a direction parallel to the alignment field is larger thanthe squareness in a hysteresis loop measured perpendicular to thealignment field. As an example, the iron nitride nanoparticles mayexhibit a squareness measured parallel to the alignment direction thatis greater than 0.50, greater than 0.75, or greater than 0.9.

As the aligned iron nitride nanoparticles include α″-Fe₁₆N₂ phasedomains, the alignment may be described more specifically according tothe magnitudes of specific peaks in an X-ray diffraction pattern.Alignment may be detected in an X-Ray diffraction pattern that presentsa preferred orientation of the (004) crystal plane α″-Fe₁₆N₂ phase. The(004) peak in an X-Ray Diffraction pattern corresponds to the c-axis ofα″-Fe₁₆N₂'s unit cell. The c-axis is the magnetic easy axis of theα″-Fe₁₆N₂ phase. Such a preferred orientation can be determined bymeasuring the relative intensity of the α″-Fe₁₆N₂ (004) peak to themost-intense α″-Fe₁₆N₂ (202) peak in a diffraction pattern, where thediffraction vector is parallel to the alignment direction.

The disclosed nanoparticles exhibit such a preferred orientation. Morespecifically, the disclosed nanoparticles exhibit a ratio of integratedintensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂(202) x-ray diffraction peak for the aligned iron nitride nanoparticlesthat is greater than at least 7%, where the diffraction vector isparallel to alignment direction. In some examples, the ratio ofintegrated intensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak toan α″-Fe₁₆N₂ (202) x-ray diffraction peak is greater than at least 50%.In yet further examples, the ratio of integrated intensities of anα″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-raydiffraction peak is greater than at least 100%.

Anisotropic iron nitride nanoparticles achieved according to the presentdisclosure may be shaped, for example, as needles, flakes, laminations,wires, thin sheets, or tapes. In further aspects, the anisotropic ironnitride nanoparticles may be joined or bonded to form bulk material,such as a bulk permanent magnet.

In certain aspects, these iron nitride particles may be comprised as ananocomposite. Such a nanocomposite may comprise a population of alignedanisotropic nanoparticles, the nanoparticles comprising an α″-Fe₁₆N₂phase; and a suitable binder. The nanocomposite may exhibit a squarenessmeasured in a parallel direction that is larger than a squarenessobserved in a perpendicular direction to the direction of alignment ofthe anisotropic nanoparticles. In further aspects, the nanocomposite mayexhibit an X-ray diffraction pattern having a ratio of integratedintensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂(202) x-ray diffraction peak that is greater than at least 7%, where thediffraction vector is parallel to the alignment direction. In someexamples, the ratio of integrated intensities of an α″-Fe₁₆N₂ (004)x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-ray diffraction peak isgreater than at least 50%. In yet further examples, the ratio ofintegrated intensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak toan α″-Fe₁₆N₂ (202) x-ray diffraction peak is greater than at least 100%.A weight fraction of the nanoparticle relative to the nanocomposite maybe in a range of from 80% to 95%, from 85% to 95%, or from 90% to 95%. Avolume fraction of the nanoparticle relative to the nanocomposite may bein a range of from 40% to 75%, 50% to 75%, or from 60% to 75%.

In yet further aspects, and as described in further detail herein, suchanisotropic iron nitride nanoparticles may be comprised as a dispersionwith a suitable solvent. The iron nitride nanoparticles may include anα″-Fe₁₆N₂ phase. The iron nitride nanoparticles may be aligned in that aratio of integrated intensities of an α″-Fe₁₆N₂ (004) x-ray diffractionpeak to an α″-Fe₁₆N₂ (202) x-ray diffraction peak for the iron nitridenanoparticles is greater than at least 7%, where the diffraction vectoris parallel to alignment direction and the dispersion exhibits asquareness measured parallel to the alignment direction that is greaterthan a squareness measured perpendicular to the alignment direction. Aweight fraction of the nanoparticle relative to the dispersion may be ina range of from 80% to 95%, from 85% to 95%, or from 90% to 95%. Avolume fraction of the nanoparticle relative to the dispersion may be ina range of from 40% to 75%, 50% to 75%, or from 60% to 75%.

Preparation of Aligned Nanoparticles and Permanent Magnets FormedThereof

A method of forming an anisotropic permanent magnet may compriseannealing an iron-containing agglomerated powder in the presence ofnitrogen to provide iron nitride nanoparticles. Iron nitridenanoparticles may be produced from iron-based precursor nanoparticlesvia a gas nitriding process that takes place at low temperatures (forexample, less than 200° C.). This process may incorporate ammonia gas totransform the precursor nanoparticles directly into an iron nitridenanoparticle that contains the α″-Fe₁₆N₂ phase. The low temperaturerange at which this nitriding process can proceed may require aniron-based precursor with high specific surface area (such asnanoparticles or nanoporous foams) because of slow reaction kinetics.

An iron-containing agglomerated powder may include, for instance, aniron-containing raw material such as iron powder, bulk iron, FeCl₃,Fe₂O₃, or Fe₃O₄. In some examples, an iron-containing raw material mayinclude substantially pure iron (such as, for example, iron with lessthan about 10 atomic percent (at. %) dopants or impurities) in bulk orpowder form. Dopants or impurities may include, for example, oxygen oriron oxide. Agglomerated powder may describe the iron-containingmaterial in a form of discrete collections of particles. Although apowder is described, the iron-containing raw material may be provided inany suitable form, such as a powder or relatively small particles. Insome examples, an average size of particles in iron containing rawmaterial may be between about 50 nanometers (nm) and about 5 micrometers(μm).

The process of annealing the iron-containing agglomerated powder mayproceed according to a number of methods to reduce the nanoparticles toelemental iron Fe. As an example, in some examples, annealing theanisotropic particles including iron nitride may include heating theparticles to a temperature between about 120° C. and about 250° C., suchas between about 120° C. and about 180° C., for example, between about120° C. and 150° C. Annealing may proceed under a nitrogen gas, such asammonia.

The process of annealing may further include passivating. Thenanoparticles may be passivated by controlled oxidation, forming a layerof iron oxide on the surface of the nanoparticles. The nanoparticles mayalso be passivated by coating the nanoparticles with another compound,such as aluminum oxide, silicon oxide, titanium oxide, aluminum nitride,and/or titanium nitride.

In some examples, the annealing process continues for between about 10hours and about 200 hours, such as between about 10 hours and about 40hours. In one example, annealing may proceed for about 20 hours. In someexamples, the annealing process may occur under an inert atmosphere,such as argon Ar or an Ar/oxygen blend, to reduce or substantiallyprevent oxidation of the iron. Further, in some implementations, whilethe anisotropic particles including iron nitride are annealed, thetemperature is held substantially constant.

In some examples, rather than being formed using a milling technique, ananisotropic particle including at least one α″-Fe₁₆N₂ phase domain maybe formed by nitriding and annealing anisotropic iron-containingprecursors. An example technique may include, for example, nitriding ananisotropic particle including iron to form an anisotropic iron nitridenanoparticle.

The iron nitride nanoparticles that have been annealed may exhibit aparticular intrinsic coercivity. As an example, the iron nitridenanoparticles may exhibit an intrinsic coercivity of about 2,000Oersteds (Oe) to 4,000 Oe. In further aspects, the iron nanoparticleshave an intrinsic coercivity from 2,500 to 4,000 Oe. In yet furtheraspects, the iron nanoparticles have an intrinsic coercivity from 3,000Oe to 4,000 Oe. Intrinsic coercivity may be measured according to anumber of methods known in the art. In a specific example, intrinsiccoercivity may be measured suing a Vibrating Sample Magnetometer (VSM).

To enhance squareness, the annealed iron nitride nanoparticles may bedispersed in a suitable fluid for further processing. A weight fractionof the iron nitride nanoparticles relative to the suitable fluid may bein a range of from 80% to 95%, from 85% to 95%, or from 90% to 95%. Avolume fraction of the nanoparticle relative to the suitable fluid maybe in a range of from 40% to 75%, 50% to 75%, or from 60% to 75%. Thesuitable fluid comprise a water-based solvent (aqueous) or an organicsolvent (non-aqueous) and one or more suitable additives. The one ormore additives may comprise a dispersing agent, a stabilizer, a wettingagent, a surfactant, a viscosity modifier, a corrosion inhibitor,emulsifier or any combination thereof.

Thus, in one aspect, the iron nitride nanoparticles may be dispersed ina solution of one or more stabilizers and water. The resultingdispersion may be subjected to a process for deagglomerating thenanoparticles via mechanical agitation, followed by freeze drying. Theseprocesses of mechanical agitation may comprise, but are not limited to,ultrasonication and/or mechanical ball milling. Here, the one or morestabilizers may comprise stearic stabilizers such as polyethyleneglycol. The one or more stabilizers may be an electrostatic stabilizer.An electrostatic stabilizer may include sodium citrate, sodiumhexametaphosphate, or citric acid. Freeze drying may proceed in thepresence of a magnetic field to further promote alignment of the ironnitride nanoparticles.

In other aspects, the annealed iron nitride nanoparticles may bedispersed in an organic solvent for further processing. Accordingly, theiron nitride nanoparticles may be dispersed in a solution of one or morestabilizers and an organic solvent, and subjected to ultrasonicationand/or mechanical ball milling. Stabilizers that may accompany theorganic solvent may comprise organic compounds. Suitable organiccompounds may include, but are not limited to, oleic acid, stearic acid,or oleylamine. The organic solvent may include a polar solvent such asmethanol or a nonpolar solvent such as heptane. A suitable polar solventmay include methanol. A suitable nonpolar solvent may include heptane.

Ultrasonication may be performed by submersing the transducer of anultrasonic probe into the nanoparticle/solvent dispersion. Theultrasonic energy may be transmitted to the nanoparticle agglomeratesvia the solvent. Ultrasonication produces cavitation in the solventwhich may occur within and around the nanoparticle agglomerates. Thecollapse of the cavities creates an effect that mechanically agitatesthe nanoparticles, providing the force needed to force the nanoparticlesapart (deagglomeration).

In some examples, the milling may be performed, for example, usingmilling spheres in the bin of a rolling mode, stirring mode, orvibration mode milling apparatus. In some examples, a temperature atwhich components are milled may be controlled to facilitate formation ofanisotropic iron nitride nanoparticles. For example, a techniqueaccording to this disclosure may include milling an iron-containing rawmaterial at a predetermined low temperature in the presence of anitrogen source using milling media.

After processing, excess fluid may be removed and the iron nitridenanoparticles may be dried according to a suitable method. Anappropriate method of drying the iron nitride nanoparticles may includefreeze drying, spray drying, debinding, solvent exchange, or anycombination thereof.

The dried iron nitride nanoparticles may be combined with a suitablebinder composition to provide a nanoparticle binder mixture. Thesuitable binder composition may comprise a polymeric material and may beincorporated to further process agglomerates of iron nitridenanoparticles. In certain aspects, the polymeric material comprises anacrylic, an acrylate, a bismaleimide, an ester, a urethane, a styrene, apolyvinyl alcohol, a polyvinyl acetate, a cellulose acetate, an ethylcellulose, a polycarbonate, a polyester, a syndiotactic polystyrene, ora combination thereof. As a specific example, a mixture of the ironnitride nanoparticles and an epoxy composition may be combined andfurther processed. The resulting iron nitride nanoparticle/epoxy mixturemay centrifugated, for example, as a way to separate nanoparticleagglomerates by size, with the smaller agglomerates exhibiting greatersquareness.

In certain aspects, the nanoparticle binder mixture may be aligned in amagnetic field. That is, in various examples, the nanoparticle bindermixture may be subjected to a magnetic field for a certain duration oftime at a particular magnetic flux density, Tesla (T).

In some examples, an applied magnetic field may be at least 0.2 T (2000Gauss). The temperature at which the magnetic field is applied may atleast partially depend upon further elemental additions to the ironnitride base composition and the approach used to initially synthesizethe iron nitride base composition. In some examples, the magnetic fieldmay be at least about 0.2 T, at least about 0.3 T, at least about 1 T,at least about 2 T, at least about 5 T, at least about 6 T, at leastabout 8 T. In some examples, the magnetic field is between about 0.2 Tand about 1 T. In other examples, the magnetic field is between about0.3 T and about 1 T. The magnetic field may be applied as a continuousstatic field or as a pulsed field.

The nanoparticle binder mixture may be cured to form a permanent magnet.In a thermoset binder, the curing process occurs by crosslinking of thepolymer molecules in the starting resin, fixing the nanoparticles inplace. In a thermoplastic binder, curing occurs by allowing the liquidbinder to cool below its glass transition temperature.

Properties and Articles

Anisotropic iron nitride nanoparticles achieved according to the presentdisclosure may be shaped, for example, as needles, flakes, laminations,wires, thin sheets, or tapes. The shape of the nanoparticle may bedetermined by the method used to form a given nanoparticle. For example,needles may be formed by nitriding nanorods. Flakes may be formed bynitriding nanoplatelets. Wires may be formed by nitriding nanofilaments.

In further aspects, the anisotropic iron nitride nanoparticles may bejoined or bonded to form bulk material, such as a bulk permanent magnet.In some examples, a workpiece may include a bulk material as described.The iron nitride materials formed by the techniques described herein maybe used as magnetic materials in a variety of applications, including,for example, bulk permanent magnets. Bulk permanent magnets may includea minimum dimension of at least about 0.1 mm. In some examples, the bulkmaterial including iron nitride may be annealed in the presence of anapplied magnetic field. In other examples, iron nitride materials maynot be bulk materials (may have a minimum dimension less than about 0.1mm), and the iron nitride materials may be consolidated with other ironnitride materials to form bulk permanent magnets. Examples of techniquesthat may be used to consolidate iron nitride magnetic materials aredescribed in the art.

In certain aspects and as provided herein, these iron nitridenanoparticles may be comprised as a nanocomposite or as a dispersion.

In any of the above examples, other techniques for consolidating of aplurality of anisotropic iron nitride nanoparticles may be used, such aspressure, electric pulse, spark, applied external magnetic fields, aradio frequency signal, laser heating, infrared heating, for the like.Each of these example techniques for joining a plurality of anisotropicparticles including iron nitride may include relatively low temperaturessuch that the temperatures used may leave any Fe₁₆N₂ phase domainssubstantially unmodified (such that Fe₁₆N₂ phase domains are notconverted to other types of iron nitride).

The present disclosure provides aligned, anisotropic iron nitridenanoparticles. As noted herein, the iron nitride nanoparticles of thepermanent may be aligned such that a ratio of integrated intensities ofan α″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-raydiffraction peak for the iron nitride nanoparticles is greater than atleast 7%, where the diffraction vector is parallel to alignmentdirection. Further, the iron nitride nanoparticles may exhibit asquareness measured parallel to the alignment direction that is greaterthan a squareness measured perpendicular to the alignment direction.

A permanent magnet comprising the disclosed aligned, anisotropic ironnitride nanoparticles may exhibit a number of enhanced properties,particularly enhanced squareness. As noted herein, the improvedsquareness may further improve performance of the permanent magnet.Improved squareness may increase the energy product by increasing thearea of the permanent magnet's hysteresis loop. Furthermore, thepermanent magnet may exhibit a higher remnant magnetization because ofthe higher squareness results in a higher density of magnetic flux linesemanating from the poles of the permanent magnet. This may result in ahigher magnetomotive force (MMF), which is usable in magnetic circuits.

A permanent magnet with a high squareness may have a linear flux v.field (B v. H) curve on the second quadrant. This property may improveresistance to demagnetization in devices with a high magnetic loading,such as electric motors and generators. Aligned magnets, such as thedisclosed magnet having enhanced squareness, may also exhibit enhancedcoercivity, further increasing the energy product. Anisotropic permanentmagnets with high squareness have higher economic value than isotropicmagnets of the same composition.

In additional embodiments, the present invention provides methods toincrease the coercivity (Hc) of iron nitride nanoparticles withoutsacrificing saturation magnetization (M_(Sat)) and establishescompositions that have higher Hc, and hence magnetic materials with ahigher energy product. This increase in Hc while not reducing M_(Sat)shifts the Hc-M_(Sat) trade-off in the direction that yields higherenergy product.

For example, certain methods utilize mechanical milling of thenanoparticle precursors. Mechanical milling adjusts the magneticproperties of the iron nitride nanoparticles produced from agglomeratediron oxide nanoparticles. Mechanical milling, as a way to reduce theaverage agglomerate size, may be used to adjust the flowability andpowder handling characteristics of powders. Without being bound by anyparticular theory of operation, it is believed that mechanical millingmay also raise the energy content of the nanoparticles by creatingdefects such as lattice vacancies and dislocations. The residual strain,partitioned among connected single nanoparticles, may make them to bemore reactive to process gasses.

Additionally, the milling methods as described herein can promote theformation of uniform phase composition throughout the nanoparticleagglomerates. This can result in a higher mass fraction of the preferredα″-Fe₁₆N₂ phase and a lower mass fraction of the deleterious α-Fe andε-Fe₂₋₃N phases. This yields compositions having a higher coercivity fora given saturation magnetization than can be obtained in iron nitridenanoparticles made without milling methods. The present disclosurerelates at least to the following aspects.

Aspect 1. A permanent magnet comprising: a plurality of aligned ironnitride nanoparticles wherein the iron nitride nanoparticles includeα″-Fe₁₆N₂ phase domains; wherein a ratio of integrated intensities of anα″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-raydiffraction peak for the aligned iron nitride nanoparticles is greaterthan at least 7%, where the diffraction vector is parallel to alignmentdirection, and wherein the iron nitride nanoparticles exhibit asquareness measured parallel to the alignment direction that is greaterthan a squareness measured perpendicular to the alignment direction.

Aspect 2. The permanent magnet of aspect 1, wherein the alignednanoparticles are configured as a wire, a thin sheet, or a tape, andwherein the wire, thin sheet, or tape are bonded to provide thepermanent magnet.

Aspect 3. The permanent magnet of aspect 1, wherein a ratio ofintegrated intensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak toan α″-Fe₁₆N₂ (202) x-ray diffraction peak is greater than at least 50%.

Aspect 4. The permanent magnet of aspect 1, wherein a ratio ofintegrated intensities of an α″-Fe₁₆N₂ (004) x-ray diffraction peak toan α″-Fe₁₆N₂ (202) x-ray diffraction peak is greater than at least 100%.

Aspect 5. The permanent magnet of aspect 1, wherein the iron nitridenanoparticles exhibit a squareness measured parallel to the alignmentdirection that is greater than 0.50.

Aspect 6. The permanent magnet of aspect 1, wherein the iron nitridenanoparticles exhibit a squareness measured parallel to the alignmentdirection that is greater than 0.75.

Aspect 7. The permanent magnet of aspect 1, wherein the iron nitridenanoparticles exhibit a squareness measured parallel to the alignmentdirection that is greater than 0.9.

Aspect 8. A dispersion comprising: iron nitride nanoparticles, whereinthe iron nitride nanoparticles include an α″-Fe₁₆N₂ phase and a solvent,wherein a ratio of integrated intensities of an α″-Fe₁₆N₂ (004) x-raydiffraction peak to an α″-Fe₁₆N₂ (202) x-ray diffraction peak for theiron nitride nanoparticles is greater than at least 7%, where thediffraction vector is parallel to alignment direction, and wherein thedispersion exhibits a squareness measured parallel to the alignmentdirection that is greater than a squareness measured perpendicular tothe alignment direction.

Aspect 9. The dispersion of aspect 8, wherein the weight fraction of thenanoparticle relative to the dispersion is in a range of from 80% to95%.

Aspect 10. The dispersion of aspect 8, wherein the weight fraction ofthe nanoparticle relative to the dispersion is in a range of from 85% to95%.

Aspect 11. The dispersion of aspect 8, wherein the weight fraction ofthe nanoparticle relative to the dispersion is in a range of from 90 to95%.

Aspect 12. The dispersion of aspect 8, wherein the volume fraction ofthe nanoparticle relative to the dispersion is in a range of from 40% to75%.

Aspect 13. The dispersion of aspect 8, wherein the volume fraction ofthe nanoparticle relative to the dispersion is in a range of from 50% to75%.

Aspect 14. The dispersion of aspect 8, wherein the volume fraction ofthe nanoparticle relative to the dispersion is in a range of from 60% to75%.

Aspect 15. The dispersion of aspect 8, wherein the solvent compriseswater and one or more additives.

Aspect 16. The dispersion of aspect 8, wherein the solvent comprises anorganic solvent and one or more additives.

Aspect 17. A nanocomposite comprising: a population of alignedanisotropic nanoparticles, the nanoparticles comprising an α″-Fe₁₆N₂phase; and a binder, wherein the nanocomposite exhibits a squarenessmeasured in a parallel direction that is larger than a squarenessobserved in a perpendicular direction to the direction of alignment ofthe anisotropic nanoparticles, and wherein the nanocomposite exhibits anX-ray diffraction pattern having a relative intensity of an α″-Fe₁₆N₂(004) peak that is greater than the intensity of the most-intenseα″-Fe₁₆N₂ (202) peak in a diffraction pattern, where the diffractionvector is parallel to the alignment direction.

Aspect 18. The nanocomposite of aspect 17, wherein the binder comprisesa polymeric material.

Aspect 19. The nanocomposite of aspect 18, wherein the polymericmaterial comprises an epoxy, an acrylic, an acrylate, a bismaleimide, anester, a urethane, a styrenic, a polyvinyl alcohol, a polyvinyl acetate,a cellulose acetate, an ethyl cellulose, a polycarbonate, a polyester, asyndiotactic polystyrene, or a combination thereof.

Aspect 20. The nanocomposite of aspect 5, wherein the weight fraction ofthe nanoparticle relative to the nanocomposite is in the range of from80% to 95%.

Aspect 21. The nanocomposite of aspect 5, wherein the weight fraction ofthe nanoparticle relative to the nanocomposite is in the range of from85% to 95%.

Aspect 22. The nanocomposite of aspect 5, wherein the weight fraction ofthe nanoparticle relative to the nanocomposite is in the range of from90% to 95%.

Aspect 23. The nanocomposite of aspect 5, wherein the volume fraction ofthe nanoparticle relative to the nanocomposite is in the range of from40% to 75%.

Aspect 24. The nanocomposite of aspect 5, wherein the volume fraction ofthe nanoparticle relative to the nanocomposite is in the range of from50% to 75%.

Aspect 25. The nanocomposite of aspect 5, wherein the volume fraction ofthe nanoparticle relative to the nanocomposite is in the range of from60% to 75%.

Aspect 26. A method of forming an anisotropic permanent magnet, themethod comprising: annealing an iron-containing agglomerated powder inthe presence of nitrogen to provide iron nitride nanoparticles whereinthe iron nitride nanoparticles have an intrinsic coercivity of about2,000 Oe to 4,000 Oe; dispersing the iron nitride nanoparticles in afluid; removing excess fluid and drying the iron nitride nanoparticles;combining the iron nitride nanoparticles with a binder composition toprovide a nanoparticle binder mixture; aligning the nanoparticle bindermixture in a magnetic field, and curing the nanoparticle binder mixtureto form a permanent magnet.

Aspect 27. The method of aspect 26, wherein the iron nanoparticles havean intrinsic coercivity from 2,500 to 4,000 Oe.

Aspect 28. The method of aspect 26, wherein the iron nanoparticles havean intrinsic coercivity from 3,000 Oe to 4,000 Oe.;

Aspect 29. The method of aspect 26, wherein the fluid is aqueous.

Aspect 30. The method of aspect 26, wherein the step of dispersing theiron nitride nanoparticles in a fluid includes: introducing the ironnitride nanoparticles to a mixture of water and one or more additives toprovide an aqueous solution; and subjecting the aqueous solution to aprocess of ultrasonication and/or wet ball milling.

Aspect 31. The method of aspect 30, wherein the one or more additivescomprises a dispersing agent, a stabilizer, a wetting agent, asurfactant, a viscosity modifier, a corrosion inhibitor, emulsifier orany combination thereof.

Aspect 32. The method of aspect 26, wherein the fluid is non-aqueous.

Aspect 33. The method of aspect 26, wherein the step of drying the ironnitride nanoparticles includes freeze drying, spray drying, debinding,solvent exchange, or any combination thereof.

Aspect 34. A permanent magnet formed according to the method of aspect26, wherein the permanent magnet exhibits a squareness measured in aparallel direction that is larger than a squareness observed in aperpendicular direction to the direction of alignment of thenanoparticles, and wherein the permanent magnetic exhibits an X-raydiffraction pattern having a relative intensity of an α″-Fe₁₆N₂ (004)peak that is greater than the intensity of the most-intense α″-Fe₁₆N₂(202) peak in a diffraction pattern, where the diffraction vector isparallel to the alignment direction.

Aspect 35. A permanent magnet formed according to the method of aspect26, wherein a ratio of integrated intensities of an α″-Fe₁₆N₂ (004)x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-ray diffraction peak forthe iron nitride nanoparticles is greater than at least 7%, where thediffraction vector is parallel to alignment direction.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompounds, compositions, articles, devices and/or methods claimed hereinare made and evaluated, and are intended to be purely exemplary and arenot intended to limit the disclosure. Efforts have been made to ensureaccuracy with respect to numbers (e.g., amounts, temperature, etc.), butsome errors and deviations should be accounted for. Unless indicatedotherwise, parts are parts by weight, temperature is in ° C. or is atambient temperature, and pressure is at or near atmospheric. Unlessindicated otherwise, percentages referring to composition are in termsof wt %.

There are numerous variations and combinations of reaction conditions,e.g., component concentrations, desired solvents, solvent mixtures,temperatures, pressures and other reaction ranges and conditions thatcan be used to optimize the product purity and yield obtained from thedescribed process. Only reasonable and routine experimentation will berequired to optimize such process conditions.

Example I: Samples 1-6

Commercially available nanoparticles of γ-Fe₂O₃ were obtained as dry,agglomerated powders. The nanoparticle agglomerates were passed througha sieve column and the 25 μm-53 μm size fraction was retained. Sevenlots of powder, each lot 2.0 grams in mass, were transformed into ironnitride nanoparticles in a rotary tube furnace. The iron nitridenanoparticles were formed by first by first reducing the nanoparticlesinto elemental iron Fe by annealing at a temperature of about 340° C.for about 17 hours in hydrogen gas flowing at about 200 standard cubiccentimeters per minute (sccm). The Fe nanoparticles were thentransformed into iron nitride by annealing at a temperature of about145° C. for 19 hours in ammonia gas flowing at about 60 sccm. Aftercooling to room temperature under flowing nitrogen, the iron nitridenanoparticles were passivated by flowing a 1% oxygen/argon mixture overthe iron nitride nanoparticles for about 2 hours at a flow rate of about2 standard cubic feet per hour (scfh). The seven lots of iron nitridenanoparticles were blended together for further processing. Theintrinsic coercivity of the blended nanoparticles was measured to be1,971 Oe. The coercivity was measured using VSM.

Approximately 1 gram of the passivated iron nitride nanoparticles wereintroduced into an aqueous solution of a stabilizer and water. Themixtures were then be milled by ultrasonication and/or wet ball milling.After milling, the excess solution was removed and the nanoparticleswere freeze dried, or washed with isopropyl alcohol. Ultrasonication wasperformed with a 200 watt probe sonicator. Wet ball milling wasperformed with a planetary ball mill, using stainless steel milling jarsand milling media, operating at 300 rpm. Table 1 provides the millingconditions, the nanoparticle oxide coating, the milling solution, andthe final treatment of the nanoparticles prior to sample preparation forSamples S1 through S5 and comparative sample CS6.

TABLE 1 Description of process conditions used in Samples S1 to S6.Milling Oxide Sample condition coating Milling solution Final treatmentS1 Ultrasonicated FeO 10% polyethylene Freeze dried for two hours glycol−400 S2 Wet ball milled FeO 10% sodium citrate Freeze dried for fourhours S3 Ultrasonicated FeO 10% polyethylene Freeze dried for two hoursglycol −400 S4 Ultrasonicated FeO Distilled water Alcohol washed for twohours S5 Ultrasonicated AlO 10% polyethylene Freeze dried for two hoursglycol −400 C56 None FeO None None

The freeze dried nanoparticles were mixed with a liquid epoxycomposition and the nanoparticles were allowed to settle to the bottomof the container. The excess liquid epoxy was removed and the remainingmixture was remixed with liquid epoxy and again allowed to settle,forming a gradient in the concentration of nanoparticles in epoxy fromthe top to bottom of the container. A sample of the nanoparticle/epoxymixture from the top of container was withdrawn and placed in a moldsituated between the poles of two permanent magnets. The magnitude ofthe magnetic field was about 5,000 Gauss. The nanoparticle epoxy mixturewas allowed to cure in the magnetic field overnight.

The cured nanoparticle/epoxy composite formed a thin disk. The disk wasabout 6 mm in diameter and about 1 mm thick. The orientation of themagnetic alignment field was perpendicular to the plane of the disk.

Comparative sample CS6 included iron nitride nanoparticles that were notultrasonicated, ball milled, or freeze dried and was made in a similarway by allowing a mixture of the nanoparticles in epoxy to cure betweenthe pole pieces of a permanent magnet.

FIG. 1 presents hysteresis loops measured from sample S5. The loops weremeasured in directions parallel to and perpendicular to the alignment.FIG. 1A shows that the squareness measured in the parallel direction waslarger than the squareness in the perpendicular direction (compare 0.53to 0.41). This phenomenon indicated that the nanoparticles in thenanoparticle/epoxy composite were at least partially aligned. Thecoercivity measured in the parallel direction was 2,376 Oe. Thecoercivity of the starting material was not recorded.

An X-Ray Diffraction pattern of the sample made from sample S5 is shownin FIG. 2 . The XRD spectrum was collected using a D5005 x-raydiffractometer with a Cu radiation source over an angular range of 25 to105° 2θ. The relative intensity of α″-Fe₁₆N₂ (004) peak is calculated bydividing the integrated intensity of α″-Fe₁₆N₂ (004) by the integratedintensity of the α″-Fe₁₆N₂ (202) peak. The relative intensity ofα″-Fe₁₆N₂ (004) peak is calculated to be 0.22. The intensity of theα″-Fe₁₆N₂ (004) peak, relative to the (202) peak, is larger (0.22) thanthe relative intensity of the α″-Fe₁₆N₂ (004) peak of a comparativesample made from nanoparticles that were not sonicated (0.11,comparative sample CS6). This indicated preferred orientation of thec-axis of the α″-Fe₁₆N₂ phase. This was a further indication that thenanoparticles in the nanoparticle/epoxy composite were at leastpartially aligned.

Hysteresis loops measured in directions parallel to and perpendicular tothe alignment field for the comparative sample CS6 are shown in FIG. 3 .FIG. 3 a shows that the squareness in the parallel direction wasslightly less than the squareness in the perpendicular direction(compare 0.41 to 0.43). This indicated that the nanoparticles in sampleCS6 were not oriented by the alignment field. The squareness measured inthe perpendicular direction (0.33) was also larger than the squarenessin the parallel direction (0.43). The coercivity measured in theparallel direction was 1,948 Oe. The coercivity of the starting materialwas not recorded.

The X-Ray Diffraction pattern of the comparative sample CS6 is shown inFIG. 4 . The diffraction vector was parallel to the alignment field. Theobserved peaks indicate a mixture of the α″-Fe₁₆N₂ (diamonds) and theα-Fe (circles) phases. The relative intensity of α″-Fe₁₆N₂ (004) peakwas calculated by dividing the integrated intensity of α″-Fe₁₆N₂ (004)by the integrated intensity of the α″-Fe₁₆N₂ (202) peak. The relativeintensity of α″-Fe₁₆N₂ (004) peak was calculated to be 0.11. The ratioof the integrated intensity of the (004) peak to the (202) peak is 0.11.This finding demonstrated the signal from a nanoparticle/epoxy compositethat was not aligned.

Example II: Samples 7-15

A second series of passivated iron nitride nanoparticles were prepared,S7 through S15. These passivated iron nitride nanoparticles having acoercivity of 2,521 Oe were sonicated in a 25% oleic acid/methanolsolution for about 120 minutes. The ultrasonication was performed with a200 Watt probe sonicator. The sonicated nanoparticles were washed twicewith methanol to remove excess oleic acid. The washed nanoparticles weremixed with epoxy. Table 2 provides the methods by which the samples wereprepared prior to magnetic alignment. Each sample was magneticallyaligned by placing it between the pole pieces of two permanent magnets.The alignment field was about 5,000 Oe. The samples were allowed to cureovernight. The aligned samples had the shape of a disk and were about 1mm in thickness and about 6 mm in diameter, with the alignment directionperpendicular to the surface of the disk.

TABLE 2 Sample preparation methods used for iron nitride nanoparticlesultrasonicated in a solution of oleic acid and methanol Sample Samplepreparation method S7 Centrifugated, sample extracted from top ofsupernatant layer S8 Centrifugated, sample extracted from bottom ofsupernatant layer S9 Centrifugated, sample extracted from decanted andstirred supernatant S10 Centrifugated, sample extracted from sedimentS11 Sample extracted from as-prepared nanoparticle/epoxy mixture S12Sample extracted from nanoparticle/epoxy mixture diluted to 1 part in 9S13 Sample extracted from nanoparticle/epoxy mixture diluted to 1 partin 27 S14 Sample extracted from nanoparticle/epoxy mixture diluted to 1part in 27 and then sonicated S15 Sample extracted fromnanoparticle/epoxy mixture diluted to 1 part in 27 and then pulsemagnetized

FIG. 5 presents hysteresis loops measured in directions parallel to andperpendicular to the alignment field direction for sample S8. FIG. 5 ashows that the squareness in the parallel direction (0.78) is largerthan the squareness in the perpendicular direction (0.40). Thisindicates that the nanoparticles in Example 8 were partially oriented bythe alignment field. The coercivity measured in the aligned directionwas 2,917 Oe, showing a substantial enhancement over the startingmaterial.

FIG. 6 presents the X-Ray Diffraction pattern of Example 8. Thediffraction vector is parallel to the alignment field. The observedpeaks indicate a mixture of the α″-Fe₁₆N₂ (diamonds) and the α-Fe(circles) phases. The relative intensity of α″-Fe₁₆N₂ (004) peak iscalculated by dividing the integrated intensity of α″-Fe₁₆N₂ (004) bythe integrated intensity of the α″-Fe₁₆N₂ (202) peak. The intensity ofthe α″-Fe₁₆N₂ (004) peak, relative to the (202) peak, was thus largerthan the relative intensity of the α″-Fe₁₆N₂ (004) peak of a comparativesample made from nanoparticles that were not sonicated (compare 0.74 to0.11 for CS6). This indicated a preferred orientation of the c-axis ofthe α″-Fe₁₆N₂ phase. This is a further indication that the nanoparticlesin the nanoparticle/epoxy composite were at least partially aligned.

Example III: Sample 16

Passivated iron nitride nanoparticles with a coercivity of 2,357 Oe weresonicated for about 120 minutes in a 10% PEG-400/water solution toprovide sample S16. After sonication, the nanoparticles were allowed tosettle and the excess solution was removed. The nanoparticles werefreeze dried overnight between the pole pieces of two permanent magnets.After freeze drying, a paste was observed to be suspended between thepole pieces of the permanent magnets. The suspended paste was mixed withepoxy, and a sample of the nanoparticle epoxy mixture was allowed tocure between the pole pieces of two permanent magnets.

Hysteresis loops measured in directions parallel to and perpendicular tothe alignment field for sample S16 are shown in FIG. 7 . FIG. 7 a showsthat the squareness in the parallel direction (0.76) was larger than thesquareness in the perpendicular direction (0.41). This indicated thatthe nanoparticles in S16 were partially oriented by the alignment field.The coercivity measured in the aligned direction was 2,357 Oe, showing aslight decrease over the starting material.

The X-Ray Diffraction pattern of S16 is shown in FIG. 8 . Thediffraction vector is parallel to the alignment field. The diamagneticcontribution from the sample holder was subtracted from the hysteresisloops. Again, the relative intensity of α″-Fe₁₆N₂ (004) peak iscalculated by dividing the integrated intensity of α″-Fe₁₆N₂ (004) bythe integrated intensity of the α″-Fe₁₆N₂ (202) peak. The intensity ofthe α″-Fe₁₆N₂ (004) peak, relative to the (202) peak, is larger (0.55)than the relative intensity of the α″-Fe₁₆N₂ (004) peak of a comparativesample made from nanoparticles that were not sonicated (0.11, CS6). Thisindicates preferred orientation of the c-axis of the α″-Fe₁₆N₂ phase.This is a further indication that the nanoparticles in thenanoparticle/epoxy composite were at least partially aligned.

Table 3 summarizes the magnetic and crystallographic measurements madeon the nanoparticle/epoxy composite samples for Examples I-III (S1-S5,CS6, S7-S16). The squareness was calculated by the formula:Squareness=Mr/MSat  (Eq. 1)where Mr is the remnant magnetization of the nanoparticle/epoxy sample(measured where applied field, H, equals 0 Oersteds) and MSat is thesaturation magnetization of the composite sample (here measured whereH=20,000 Oersteds). Mr was measured using a Vibrating SampleMagnetometer (VSM). The squareness was measured from magnetizationcurves measured in directions parallel and perpendicular to thedirection of the alignment field. A difference in the parallel andperpendicular squareness is a measure of the magnetic anisotropy of thesample. The Nanoparticle Br is a calculation of the remnantmagnetization of the iron nitride nanoparticles (not including theepoxy) measured parallel to the alignment field. The relative intensityof the (004) X-Ray diffraction peak is calculated as the ratio of the(004) and (202) X-ray diffraction peaks for the α″-Fe₁₆N₂. In thesemeasurements, the diffraction vector was parallel to the alignmentdirection. The relative intensity of the (004) peak for a randomlyoriented sample of iron nitride nanoparticles would be 0.07. Thus, arelative intensity of the (004) peak greater than 0.07 indicates thatcrystal lattice of the iron nitride nanoparticles is preferentiallyoriented parallel to the alignment direction.

Table 3 also provides magnetic measurements of the aligned nanoparticlesafter they are put into the epoxy to form a bonded permanent magnet. Themeasure of the nanoparticle magnetization here is Br. This is theremnant magnetization that is produced once a field is applied to theepoxy-bonded sample and removed. Higher Br generally gives rise tobetter magnets. Br is a function of both the saturation magnetizationand the squareness. Saturation magnetization is calculated by dividingthe Br values in the table by the Squareness measured in the paralleldirection using Eq. 1. This calculation gives rise to a range of MSatvalues between 12.5 and 14 kG, which values can be used to characterizethe saturation magnetization of the nanoparticles in the bondedpermanent magnets.

TABLE 3 Squareness of hysteresis loops measured directions parallel andperpendicular to the alignment field; Remanence, Br, of iron nitridenanoparticles, Intrinsic coercivity of nanoparticle; IntegratedIntensity of α″-Fe₁₆N₂ phase (202) and (004) diffraction peaks; relativeintensity of (004) peak. Intrinsic Integrated Integrated RelativeSquareness Squareness Nanoparticle Coercivity Intensity IntensityIntensity Ex. Parallel Perpendicular Br (kG) (Oe) (202) (004) (004) 10.49 0.39 6.5 2,015 406.9 115.0 0.28 2 0.47 0.42 6.0 2,271 639.9 141.40.22 3 0.48 0.41 2,106 383.4 50.9 0.13 4 0.48 0.41 2,125 386.5 71.8 0.195 0.53 0.41 2,376 174 39.1 0.22 6 0.47 0.42 1,948 639.9 141.4 0.11 70.80 0.44 11.2 2,954 45.8 25.5 0.57 8 0.78 0.40 10.9 2,917 123.4 91.50.74 9 0.80 0.44 11.2 2,931 88.4 45 0.51 10 0.68 0.35 9.5 2,867 581.7478.5 0.82 11 0.66 0.35 9.2 2,882 659 477.8 0.72 12 0.68 0.38 9.5 2,886300.8 106.2 0.35 13 0.73 0.41 10.2 2,901 143.6 55.3 0.39 14 0.66 0.369.2 2,883 879.7 516.9 0.59 15 0.67 0.35 9.4 2,877 487.4 332.5 0.68 160.76 0.41 9.5 2,238 13.6 7.0 0.55

In other embodiments mechanical milling methods promote the formation ofuniform phase composition throughout the nanoparticle agglomerates,which results in a higher mass fraction of the preferred α″-Fe₁₆N₂ phaseand a lower mass fraction of the deleterious α-Fe and ε-Fe₂₋₃N phases.The combination of uniform phase composition and increased amount ofpreferred a″-Fe₁₆N₂ phase yields higher coercivity for a givensaturation magnetization compared to conventional iron nitridenanoparticles made without the milling methods. A number of processesare described throughout this disclosure. Iron nitride nanoparticles,compositions, and magnetic materials made using these processes willhave improved magnetic properties, such as higher coercivity, higherenergy product, and the like, compared to comparable iron nitridenanoparticles, compositions, and magnetic materials made without suchprocessing.

For example, in one embodiment agglomerated iron oxide nanoparticles aremechanically milled prior to reduction, nitriding, and passivationsteps. The agglomerates of iron oxide nanoparticles are received as dryagglomerates. The agglomerates are comprised of large numbers of ironoxide nanoparticles that have particle diameters in the range from 1 and100 nanometers. The agglomerates are in the range from 1 to 200micrometers in diameters and have porosities that range from 10 to 90volume percent. Within the agglomerates, the nanoparticles are boundtogether by a combination of chemical, electrostatic, magnetic, and/orfrictional forces.

As to the mechanical milling, any form of mechanical milling may becontemplated to deagglomerate the nanoparticles. For example, mechanicalmilling of the iron oxide agglomerates may be achieved by any ofultrasonication in a fluid, ball milling in the presence of a fluid, dryball milling, high shear mixing in the presence of a fluid, jet millingin a high velocity gas flow, or some combination thereof. The fluid maybe water, an organic solvent, or another fluid that can carry thenanoparticle agglomerates. The fluid may contain a surfactant to promotethe deagglomeration of the nanoparticles. The fluid may be removed aftermilling by any of drying methods such as freeze drying and/or spraydrying. The agglomerated iron oxide nanoparticles may be sieved throughbefore or after the milling process. The temperature of the millingprocess may be controlled to avoid overheating or sintering of thenanoparticles. For example, the temperature may be controlled byimmersing the milling container in an ice bath. Alternatively, apurposely designed cryomilling equipment may be utilized.

The effect of the milling process is to reduce the average size of theagglomerated iron oxide nanoparticles. The agglomerate size may beexpressed as Dx, determined as the diameter below which x % of thecumulative size distribution is contained. Often, the agglomerate sizeis expressed as D₅₀, determined as the diameter below which 50% of thecumulative size distribution is contained. For example, a D₅₀ means that50% of all particles have a particle size which is equal to or less thanthe value indicated. Correspondingly, a D99 means that 99% of allparticles have a particle size which is equal to or less than the valueindicated. The agglomerate size distribution may be measured by laserdiffraction, dynamic light scattering, optical microscopy and/orelectron microscopy.

The effect of the milling process may also introduce crystalline defectssuch as vacancies, dislocations, strain gradients inside of thenanoparticle agglomerates, and may also reduce the strength of theinterparticle bonds that form due to partial sintering. The straininduced in the agglomerates during milling may be helpful for later gasreduction and nitriding because it may cause micropores to form withinthe nanoparticles.

In another embodiment, agglomerated iron nanoparticles are mechanicallymilled after the reduction step is completed but before the nitridingstep is performed. The iron nanoparticles may be exposed to reducingspecies. For example, a hydrogen reduction step may be applied prior tonitriding the iron nanoparticles, which creates micro-channels toenhance nitrogen diffusion. The iron nanoparticles may be exposed to H₂at a temperature between about 200° C. and about 500° C. for up to about24 hours. In some examples, the material may be exposed to H₂ at atemperature of about 300° C. or higher. A flow rate of hydrogen sourceduring the hydrogen reduction may be about 100 standard cubiccentimeters per minute (sccm) or higher. In some examples, a flow rateof hydrogen source during the hydrogen reduction may be about 400standard cubic centimeters per minute (sccm) or higher. In otherexamples, as the reactor vessel size and amount of particles increasesfrom grams to kilograms, a flow rate of hydrogen source during thehydrogen reduction may be greater than 400 sccm and as high as 10 litersper minute (lpm) or higher. The mechanical milling process may fully orpartially reverse any sintering of the iron nanoparticles that mighthave occurred during the reduction step. Dry milling methods, such asdry ball milling, are contemplated to avoid reoxidation and/orcontamination of the iron nanoparticles prior to nitriding. The dry ballmilling may be performed in an inert atmosphere, such as nitrogen,argon, and/or helium, in order to prevent oxidation of the ironnanoparticles.

In another embodiment, agglomerated iron nitride nanoparticles aremechanically milled after the nitriding is completed but before anyfurther coatings and/or passivation layers are placed on the surfaces ofthe iron nitride nanoparticles. Nitriding the iron nanoparticles mayinclude exposing the iron nanoparticles to an atomic nitrogen substance,which diffuses into the iron nanoparticles. In some examples, the atomicnitrogen substance may be supplied as diatomic nitrogen (N₂), which isthen separated (cracked) into individual nitrogen atoms. In otherexamples, the atomic nitrogen may be provided from another atomicnitrogen precursor, such as ammonia (NH₃). In other examples, the atomicnitrogen may be provided from urea (CO(NH₂)₂). The nitrogen may besupplied in a gas phase alone (e.g., substantially pure ammonia ordiatomic nitrogen gas) or as a mixture with a carrier gas. In someexamples, the carrier gas is argon (Ar). In this embodiment, themechanical milling process may fully or partially reverse any sinteringof the nanoparticles that may occur during the reduction and nitridingsteps.

Coating and/or passivation may stabilize the milled particles andprevent reagglomeration. Surface oxidation can be reduced by use ofsurface passivation methods. While not wishing to be bound by anytheory, reducing or substantially preventing oxidation of the ironnitride particles may contribute to improved magnetic properties of theannealed iron nitride nanoparticles, such as coercivity, magnetization,and the like. In some examples the iron nitride nanoparticles can becoated. Suitable coatings include carbon and boron. In other examples,the coating may be aluminum oxide, or Copper metal, or Aluminum metal.The coating may be deposited using Atomic Layer Deposition. Dry millingmethods, such as dry ball milling, are contemplated to avoid reactionand decomposition of the iron nitride nanoparticles. The dry ballmilling may be performed in an inert atmosphere, such as nitrogen,argon, and/or helium, in order to prevent oxidation of the iron nitridenanoparticles.

In yet another embodiment, the agglomerated iron nitride nanoparticlesmay be mechanically milled after passivation but prior to magneticalignment. Annealing iron nitride nanoparticles in the presence of anapplied magnetic field may enhance the Fe₁₆N₂ phase domain formation inthe iron nitride nanoparticles. Increased volume fractions of α″-F₁₆N₂phase domains may improve the magnetic properties of core-shellnanoparticles including iron nitride. Improved magnetic properties mayinclude, for example, coercivity, magnetization, and magneticorientation.

In certains embodiments, the mechanical milling process can increase themagnetic anisotropy of the agglomerated iron nitride nanoparticles byfully or partially deagglomerating them to their discrete single crystalcomponents. The mechanical milling of the iron nitride agglomerates canbe suitably achieved by ultrasonication in a fluid, ball milling in thepresence of a fluid, dry ball milling, high shear mixing in the presenceof a fluid, jet milling, and the like, or some combination of thesemethods. The fluid may be aqueous (e.g., water or water-containing),non-aqueous (e.g., an organic solvent, or containing an organicsolvent), or another fluid in which the nanoparticle agglomerates can bedispersed, as well as combinations thereof. The fluid may have asurfactant, dispersing agent, or both, added to it to promote thedeagglomeration of the nanoparticles and/or to prevent thereagglomeration of the nanoparticles. The fluid may be removed aftermilling by any of drying methods such as freeze drying and/or spraydrying. The effect of the milling process is to reduce the average sizethe agglomerated iron oxide nanoparticles. The mechanical milling may bedone at milling energies sufficient to deagglomerate the nanoparticlesbut not high enough to disrupt the passivation layer coating the ironnitride nanoparticles. The agglomerated iron nitride nanoparticles maybe sieved through before or after the milling process. The milled ironnitride nanoparticles may be subjected to an additional passivationand/or coating step to repair any damage to the oxide shells sustainedduring the milling process. As previously mentioned, iron nitridenanoparticles, compositions, and magnetic materials made using theaforementioned processes will have improved magnetic properties, such ashigher coercivity, higher energy product, and the like, compared tocomparable iron nitride nanoparticles, compositions, and magneticmaterials made without such processing.

The milling media and containers used during wet and dry ball milling ofnanoparticles may themselves be magnetic or non-magnetic. In somesituations, the use of magnetic milling media and containers may bepreferred because they may help avoid sedimentation of the nanoparticlesin crevices of the milling containers. In other situations, the use ofnon-magnetic milling media and containers may be contemplated as a wayto increase milling efficiency and yield by helping to minimize magneticagglomeration of the nanoparticles.

In yet another embodiment, milling steps may be performed at anycombination of steps in the process. In one example, milling could beperformed prior to reduction and after nitriding. In another example,milling could be performed prior to reduction and after nitriding andafter passivation.

Some modifications of the process may be contemplated to prepare theagglomerated iron oxide nanoparticles as precursors. If the iron oxidenanoparticles are made by chemical means, then a capping agent may beused to arrest the growth of the nanoparticles and preventagglomeration. Alternatively, a digestive ripening method may be used tochemically modify the iron oxide nanoparticle size distribution. If theiron oxide nanoparticles are made by vapor-phase condensation, then theprocessing methods may be adjusted to promote the formation of sphericalnanoparticles with a narrow particle size distribution.

Generally, higher milling energies are needed to produce and/or modifythe nanoparticles than to deagglomerate clumps of nanoparticles. Themechanical milling methods in the present invention generally tend todeagglomerate clumps of nanoparticles and also beneficially change thebehavior of the nanoparticles during the reduction, nitriding,passivation, and/or alignment operations.

FIG. 9 shows four different materials processing schemes for making ironnitride magnets. Scheme #1 depicts milling of agglomerated iron oxidenanoparticles before reduction and nitriding. Scheme #2 depicts millingof agglomerated nanoparticles after reduction and before nitriding.Scheme #3 depicts milling of agglomerated nanoparticles after nitridingand before coating/passivation. Scheme #4 depicts milling ofagglomerated nanoparticles after coating/passivation and before magneticalignment.

FIG. 10 shows deagglomeration of nanoparticles in accordance toexemplary embodiments. Mechanical milling methods such asultrasonication and/or ball milling (wet & dry) of gamma-iron oxidenanoparticles supplied as dry agglomerates are quite effective atreducing the particle size and size distribution if the agglomerates.

FIG. 11 presents a description of agglomerated nanoparticles. Tightlybound agglomerates are made up of a plurality of nanoparticles that arephysically joined. Loosely bound agglomerates of nanoparticles arecharacterized as having the nanoparticles attracted to one another(flocculate), but not physically joined. Stabilizers desirably help toprevent flocculation such that the size distribution of the iron oxidenanoparticles are on the order of tens of nanometers in size.

FIG. 12 describes the measurement of the size of agglomeratednanoparticles, flocculated nanoparticles, and primary (small)nanoparticles using Laser Diffractometry. Sonication breaks apart theloosely bound agglomerates of iron oxide nanoparticles. Sonication instabilizer desirably creates primary (small) iron oxide nanoparticles.Measurements: 1. Starting point. 2. Particles flocculate to original“equilibrium” state even if they separate during sonication. 3.Sonication breaks apart loosely bound agglomerates, and stabilizerprevents flocculation which is when we start to see the small particles.

FIG. 13 shows the range of saturation magnetization and coercivity of aplurality of anisotropic iron nitride nanoparticles. The circled datapoints have the needed combination of Msat and Hci, i.e. MSat is >190emu/g and Hc is greater than 2,500 Oe.

FIG. 14 shows the effect of milling on the alpha″ % in core versusalpha-Fe % in core phase distribution in the iron nitride nanoparticles.Sonicated nanoparticles according to the methods described herein giverise to iron nitride nanoparticles having greater than 70% alpha″ phase.Mossbauer spectroscopy is used to determine fraction of Fe atoms inα-Fe, α″-Fe₁₆N₂, ε-Fe₂₋₃N, and superparamagnetic Fe oxide andsuperparamagnetic Fe nitride phases. “α″ in core” is calculated as Featoms in α″-Fe₁₆N₂ phase divided by Fe atoms in all non-oxide phases.“α-Fe in core” is calculated as Fe atoms in α-Fe divided by Fe atoms inall non-oxide phases. Fe atoms distributed among in ε-Fe₂₋₃N phase andoxide phase based on function derived from total fraction of atoms insuperparamagnetic phases. “D50” is total volume fraction of milled ironoxide nanoparticle agglomerates with diameter less than 50 microns.Symbols denote milling method applied to iron oxide nanoparticles priorto nitriding.

The present disclosure relates at least to the following additionalaspects.

Aspect 36. A method for producing iron nitride nanoparticles,comprising: carrying out a step of mechanical milling iron-containingnanoparticles, and a step of aligning the milled iron-containingnanoparticles in presence of magnetic field.

Aspect 37. The method according to Aspect 36, wherein theiron-containing nanoparticles are in a form of agglomerates of theiron-containing nanoparticles prior to the mechanical milling.

Aspect 38. The method according to Aspect 36, further comprising:carrying out a step of reducing the iron-containing nanoparticles inpresence of a reducing species.

Aspect 39. The method according to Aspect 38, wherein the reducingspecies comprises hydrogen.

Aspect 40. The method according to Aspect 38, wherein the mechanicalmilling is carried out prior to the reducing step.

Aspect 41. The method according to Aspect 38, further comprising:carrying out a step of nitriding the iron-containing nanoparticles inpresence of an atomic nitrogen substance to obtain iron nitridenanoparticles.

Aspect 42. The method according to Aspect 41, wherein the mechanicalmilling is carried out after the reducing step but before the nitridingstep.

Aspect 43. The method according to Aspect 41, further comprising:carrying out after the nitriding step, a step of coating theiron-containing nanoparticles with any of carbon and boron, aluminumoxide, Copper metal, Aluminum metal, wherein the iron-containingnanoparticles comprise iron nitride nanoparticles.

Aspect 44. The method according to Aspect 43, wherein the mechanicalmilling is carried out after the nitriding step but before the coatingstep.

Aspect 45. The method according to Aspect 36, wherein the mechanicalmilling is carried out by any of ultrasonication in a fluid, ballmilling in presence of a fluid, dry ball milling, high shear mixing inpresence of a fluid, and jet milling in a high velocity gas flow.

Aspect 46. The method according to Aspect 36, further comprising:immersing a milling container in an ice bath after the mechanicalmilling, wherein the mechanical milling is carried out in the millingcontainer containing the iron-containing nanoparticles.

Aspect 47. The method according to Aspect 45, wherein any of the fluidscomprises water, an organic or both.

Aspect 48. The method according to Aspect 45, wherein any of the fluidscomprises a surfactant to promote deagglomeration of the iron-containingnanoparticles.

Aspect 49. The method according to Aspect 45, wherein the dry ballmilling is carried out in an inert atmosphere comprising any ofnitrogen, argon, and helium.

Aspect 50. The method according to Aspect 43, wherein the mechanicalmilling is carried out after the coating step.

Aspect 51. The method according to Aspect 36, wherein the magneticallyannealed iron-containing nanoparticles have D50 of 25 um or less.

Aspect 52. The method according to Aspect 36, wherein the magneticallyannealed iron-containing nanoparticles have D50 of 10 um or less.

Aspect 53. The method according to Aspect 36, wherein the magneticallyannealed iron-containing nanoparticles have D50 of 2.5 um or less.

Aspect 54. The method according to Aspect 36, wherein the mechanicalmilling is carried out in presence of magnetic medium.

Aspect 55. Agglomerates of iron nitride nanoparticles obtained by themethod of Aspect 36, wherein at least one of iron nitride nanoparticlescomprises α″-Fe16N2 phase domain.

Aspect 56. A plurality of anisotropic iron nitride nanoparticles, theplurality of anisotropic iron nitride nanoparticles being characterizedas having a saturation magnetization, MSat, >190 emu/g and coercivity,Hc, greater than 2,500 Oe.

The plurality of anisotropic iron nitride nanoparticles of claim 18,wherein the weight percent of the a″-Fe16N2 phase is at least 70%

Aspect 57. The plurality of anisotropic iron nitride nanoparticles ofAspect 56, wherein the plurality of anisotropic iron nitridenanoparticles are further characterized as having a uniform phasecomposition throughout, wherein the plurality of anisotropic ironnitride nanoparticles comprises a higher mass fraction of α″-Fe16N2phase and a lower mass fraction of α-Fe and ε-Fe2-3N phases.

Aspect 58. The plurality of anisotropic iron nitride nanoparticles ofAspect 57, wherein the weight percent of the α″-Fe16N2 phase is at least70%, at least 75%, or at least 80%.

Aspect 59. The plurality of anisotropic iron nitride nanoparticles ofAspect 56, wherein the iron nitride nanoparticles are coated with one ormore of carbon, boron, aluminum oxide, copper metal, or aluminum metal.

Aspect 60. A permanent magnet, comprising a plurality of iron nitridenanoparticles, the permanent magnet being characterized as having asaturation magnetization, MSat, in the range of from about 12.5 to about14 kG.

Aspect 61. The permanent magnet of Aspect 60, wherein the iron nitridenanoparticles are magnetically aligned and bonded in a matrix.

Aspect 62. The permanent magnet of Aspect 60, wherein the nanoparticlesare further characterized as having a uniform phase compositionthroughout, wherein the nanoparticles comprises a higher mass fractionof the preferred α″-Fe16N2 phase and a lower mass fraction of α-Fe andε-Fe2-3N phases.

Aspect 63. The permanent magnet of Aspect 62, wherein the weight percentof the α″-Fe16N2 phase is at least 70%, 75%, 80%.

Aspect 64. The permanent magnet of Aspect 60, wherein the iron nitridenanoparticles are coated with one or more of carbon, boron, aluminumoxide, copper metal, or aluminum metal.

Aspect 65. The permanent magnet of Aspect 60, wherein at least a portionof the iron nitride nanoparticles are characterized as beingdeagglomerated discrete primary particles.

Various examples have been described. These and other examples arewithin the scope of the following claims.

When ranges are used herein for physical properties, such as molecularweight, or chemical properties, such as chemical formulae, allcombinations, and sub-combinations of ranges for specific embodimentstherein are intended to be included.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in its entirety.

Those skilled in the art will appreciate that numerous changes andmodifications can be made to the preferred embodiments of the inventionand that such changes and modifications can be made without departingfrom the spirit of the invention. It is, therefore, intended that theappended claims cover all such equivalent variations as fall within thetrue spirit and scope of the invention.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otheraspects can be used, such as by one of ordinary skill in the art uponreviewing the above description. The Abstract is provided to comply with37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain the natureof the technical disclosure. It is submitted with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed aspect. Thus, the followingclaims are hereby incorporated into the Detailed Description as examplesor aspects, with each claim standing on its own as a separate aspect,and it is contemplated that such aspects can be combined with each otherin various combinations or permutations. The scope of the disclosureshould be determined with reference to the appended claims, along withthe full scope of equivalents to which such claims are entitled.

What is claimed is:
 1. A dispersion comprising: iron nitridenanoparticles, wherein the iron nitride nanoparticles include anα″-Fe₁₆N₂ phase and a solvent, wherein a ratio of integrated intensitiesof an α″-Fe₁₆N₂ (004) x-ray diffraction peak to an α″-Fe₁₆N₂ (202) x-raydiffraction peak for the iron nitride nanoparticles is greater than atleast 0.19, where the diffraction vector is parallel to alignmentdirection, and wherein the dispersion exhibits a squareness measuredparallel to the alignment direction that is greater than a squarenessmeasured perpendicular to the alignment direction.
 2. The dispersion ofclaim 1, wherein the weight fraction of the nanoparticle relative to thedispersion is in a range of from 80% to 95%.
 3. The dispersion of claim2, wherein the weight fraction of the nanoparticle relative to thedispersion is in a range of from 85% to 95%.
 4. The dispersion of claim2, wherein the weight fraction of the nanoparticle relative to thedispersion is in a range of from 90 to 95%.
 5. The dispersion of claim2, wherein the volume fraction of the nanoparticle relative to thedispersion is in a range of from 40% to 75%.
 6. The dispersion of claim2, wherein the volume fraction of the nanoparticle relative to thedispersion is in a range of from 50% to 75%.
 7. The dispersion of claim2, wherein the volume fraction of the nanoparticle relative to thedispersion is in a range of from 60% to 75%.
 8. The dispersion of claim2, wherein the solvent comprises water and one or more additives.
 9. Thedispersion of claim 2, wherein the solvent comprises an organic solventand one or more additives.